Studies of Electroweak Interactions and Searches for New Physics Using Photonic Events with Missing Energy at the Large Electron-Positron Collider Marat Gataullin November 22, 2005

BGO Electromagnetic Calorimeter Barrel: 7680 crystals, 2x24 rings of 160 crystals. Endcaps: 1527 crystals, 17 rings of crystals each.

BGO Energy Reconstruction Narrow profile -- 94% in S 9 To correct for leakage define:

BGO Performance at the Beginning of LEP Data 4 events, MC 0.5 Beam tests in :

RFQ Calibration System keV H - ion source (output current 7.5 mA) MeV RFQ accelerator (transmission 75%) 3. Steering and focusing magnets 4. Nitrogen-cell beam neutralizer (efficiency 60%) Output H 0 flux up to 4 mA Output H 0 flux up to 4 mA

RFQ System

RFQ Concept Radiative capture of protons produces a flux of 17.6 MeV photons Simultaneous calibration of the entire BGO calorimeter RFQ runs performed twice each year, no major hardware problems. BGO calorimeter in standby mode. Average trigger rate of 80 Hz, giving 20 million triggers after 4 days.

RFQ Occupancy

RFQ Calibration HH+ defined as a point half-way below and to the right of the calibration maximum

RFQ Calibration Constants

RFQ-Only Calibration with 45 GeV Bhabha electrons RFQ-Only Calibration with 45 GeV Bhabha electrons However, statistical precision was found to be about 1%. Significant systematic effects from variations in the photon incident angle and energy extrapolation. Solution: use Bhabha electrons to set the absolute scale.

Bhabha Calibration Sample Select back-to-back events. Shower-shape cuts also applied. LEP calibration runs days/year and L=4pb/year. 50k showers in the barrel and 850k showers in the endcaps.

RFQ+Bhabha Calibration Algorithm  Starting set of constants provided by the RFQ calibration.  Typically only 4-5 iterations required to converge.  Robust, now used in CMS calibration studies.  Easy to implement corrections for dead crystals.

Calibration Results Also checked with π and η two-photon decays

Dead Crystals  About 1.5% of all BGO channels were malfunctioning  12% of selected showers had a dead crystal in 3x3 matrix  5% were on the edges between the barrel and endcaps  Energy loss taken into account both during the calibration and physics analysis and physics analysis

Dead Crystals

BGO Aging Checked using 45 GeV Bhabhas, source unknown. Loss of about -0.5% per year.

BGO Non-Linearity Checked using Bhabhas with energies between 45 and 103 GeV. Going from 45 and 103 GeV increased the BGO response by about 0.4%. Overall conclusion: the energy scale was known to better than 0.3%.